


Wrong room

by iimbe2iile



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell (Undertale), F/M, Ive really been feeling water sex lately, Masturbation, Reader Is Not Frisk, Reader is female and in college, Underfell Sans (Undertale), Water Sex, a few... years? after monsters come to the surface
Language: English
Status: Completed
Published: 2019-06-06
Updated: 2019-06-06
Packaged: 2020-04-11 21:01:43
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,058
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19117624
Author URL: https://archiveofourown.org/users/iimbe2iile/pseuds/iimbe2iile
Summary: Sans kinda freaks you out a little bit, but you've been warming up to him over the months. Things are going pretty well--that is until you accidently walk in on him... doing something you did NOT know a skeleton could do.---MALE/PENIS VERSION NOW AVAILABLE ON MY PAGE!!!





	Wrong room

**Author's Note:**

> Had to make a seperate account for stuff like this because my friend found my usual account and I dont wanna have to deal with that.  
> I've really been feeling water sex lately, so here's this. I wanna do another one shot about pool stuff, so we'll see if I get around to that. Anyhow, enjoy.

A lot of things have been stressing you out lately. College graduation is sneaking up on you faster than you could've ever imagined; your friends have been letting a lot of new people into your friend group, forcing you to socialize; you've been trying to lay off drinking and focus on keeping your life together at least until school is over so you won't have to retake a whole year…

But mostly you're stressed out about this whole Sans situation.

Sans is someone who you've always kind of seen roaming around campus even though he isn't a student, usually dicking around and harassing students with other assholes. He somehow made his way into your friend group through this shithead named Carter and he's been tagging along on all of your friendventures since. You only really started talking to him a few months ago and yeah, he's kind of an asshole, but secretly a big softy. 

Oh yeah, and he's a skeleton.

You're not going to lie, you were terrified at first when he started hanging around you. He had big, comically sharp teeth and glowing red eyes. Other monsters never bothered you much, but something about seeing a walking, talking human-like skeleton rubbed you the wrong way. But after a few months, the guy started to grow on you.

And then the whole thing happened.

Yesterday, Carter's bitch girlfriend Gina invited you and all your friends to hang out at her parents' cabin and of course you said yes because it's a fucking cabin--how cool is that? You've always loved the idea of staying up in the woods, away from the rush of the city. 

You all had a pretty good time going up there and getting settled in for the week. Gina half-heartedly showed you all around, nonchalantly gesturing to animal heads lining the walls and flat screen tvs and a flowing river that went under the house and out to a small lake like it was any other part of a normal house. Matthew made dinner and you all sat next to a fireplace and watched stupid horror top ten videos on YouTube and played drinking games until everyone slowly waned out and headed to bed: first Matthew and his girlfriend Katie, then Parker and his buddy Peter, then Sans, then Harry, and lastly you once Carter and Gina started getting annoyingly handsy.

You walked up the stairs and down a hallway to what you _thought_ was your room. You turned the handle and stepped inside and when you looked up you were surprised to see Sans sitting on the bed. Not only that, but his hand was placed on a long, glowing red member between his legs that he was frantically stroking and jerking. It took you a few moments of staring before you realized what was happening but by then he had already looked up and locked eyes with you.

His hand froze in place and you were both silent, both equally as fucking shocked. He opened his mouth to say something but you were already closing the door.

You took a moment to collect yourself before rushing to the room a door over and locking yourself in for the night.

Now you couldn't sleep and were dreading tomorrow. You aren't even a day into this trip and you walked in on someone masturbating. 

You've been thinking about it all night. You knew that monsters like him could have sex, but you've only ever heard about them using weird soul magic. You never would've guessed they had magical dicks. 

What would you say to him when you saw him? There's no easy way out. You can't ghost him because he's friends with everyone you hang out with and that'd be a whole ordeal. Maybe you could just pretend it didn't happen, but Sans wasn't exactly the kind of person to let things go easily.

Sighing, you stood up. It was now past midnight and there was no way you were getting to sleep. You needed some air.

You got up, slipped on some shoes and tiptoed outside, carefully eyeing Sans' door the whole way down the stairs. The last thing you wanted was an awkward late-night encounter. 

Quietly sneaking through the side door, you made your way into the warm Summer night. You walked across the deck, peering down at the small river that flowed into one end of the house and out the other. You figured now was as good a time as any to go check out that lake, so you made your way down the deck stairs and clumsily tripped down the muddy trail.

It was a dark night, but there was a deep blue gradient that stretched across the sky that provided a beautiful backdrop for infinite twinkling stars. You always forgot how pretty the sky is outside the city.

Before you knew it, you reached the end of the trail and were on a small stretch of land that faded into an inky-black lake. The moon and stars reflected off of the water's surface, dispersing into small, milky ripples at the smallest disturbance. You broke a small smile, temporarily forgetting why you even came out here. 

"what, you followin' me now?" 

You jumped at the sound of a deep voice, letting out a surprised shout. You swiveled to the side, your face lighting on fire.

"Sans?"

"the fuck're you doin' out here?" He was standing a few feet to your right, his hands buried deep in the pockets of his coat. 

"I, uh, I was…" You swallowed. You really wanted more time to think about your response to all of this but guess not. "I couldn't sleep."

"i tend ta do that to people," he smirked. 

You glared and got ready to remark on how bold he was to already joke about this, but hesitated when his smile twitched under a blush of his own. Sans never seemed like one to get flustered easily, but you had to guess that what happened would embarrass almost anyone.

"Shut up," you huffed, looking back at the lake. 

You both stood in silence. 

You figured you should probably clear this up while you had the chance and, despite unprecedented, this seemed like the perfect chance. After a few beats, you shuffled over to stand next to him.

He stared forward even as you glanced over at him, unwilling to meet your gaze. Your eyes drifted down from his face and over his body, snapping back up once you reached his pantline. A stupid part of your mind couldn't help but wonder what he was packing down there but you very quickly pushed the thought away, clearing your throat. 

"Sorry. Uh, about earlier," you mumbled. "It was an accident. My room was one door over so I thought it was mine and uh. Sorry." 

He looked over, his eyes quickly shooting away when he met your gaze. "s'fine," he grumbled back. 

Looking at him, you noticed what an unnatural red it was that adorned his cheekbones. It was bright, almost fluorescent under the moonlight. That must be the colour of his magic? You weren't exactly all that sure how magic worked, but his blush was the same colour as…

Your mind snapped back to you walking in on him. That few seconds before he saw you where his head was doubled back in pleasure and you just watched him.

This time the heat in your body shot through your spine and settled between your legs at the memory and the shock of that was enough to make you snap your gaze away from him. 

You weren't actually turned on by this, were you? Come on.

You listened to Sans uncomfortably shift beside you, his hands restlessly turning in his pockets.

"I, uh, actually came out here to swim." He finally looked over at you, a curious expression on his face. You weren't sure why you said that. It just came out.

"s'freezing."

You shrugged. "I dunno, it's kind of nice out."

"the water, i mean."

Oh yeah. Probably. "Nah. It'll be nice. You get used to it pretty quick." 

"suit yerself, sweetheart." It was a nickname he used universally, but this time it send a wave of… something down your body. 

This was stupid. This whole thing was dumb, but suddenly you kind of had your heart set on it. Seducing him, you mean. 

You stepped forward a few steps, taking a deep breath. You were taking a big gamble here on whether he'd be into this. If not, he'd probably think you were one big class creep. 

Apparently you were willing to take your chances because your hands both slowly rose up to grip the bottom of your shirt. You took a few more beats to hesitate before you lifted up your shirt over your head, tossing it to the side. Your hands met the top of the jeans you never changed out of, undoing the button and zipper. You waited the longest before finally letting go and letting them drop to your ankles. You shimmied them off of your feet along with your shoes, looking out intently at the water.

Now standing in just your underwear, you very slowly glanced behind you.

Sans was still standing there, watching you intently. The lights in his eyes had gone black so you couldn't tell where he was looking or if that meant he had done the skeleton equivalent of closing his eyes, but you saw a bright blush covering his entire face. His mouth was slightly open, something resembling a tongue trailing along his sharp teeth.

You took one last glance at him over your shoulder. "Feel free to join me." And then you turned back around, walking toward the water. You flinched at first contact; the water was a lot colder than you expected, but still manageable. It actually did seem like a perfect night to swim. You continued forward, eventually walking in far enough that the water reached up to your shoulders. 

Shivering, you closed your eyes. You gently paddled in place, taking in the feeling of the water. You actually did get used to it pretty fast.

Opening your eyes, you were surprised to find Sans pulling his coat over his shoulders.

You closed your eyes, listening to the rustling of his clothes. Not a minute later, you heard almost silent ripples of water as he walked into the lake, submerging himself. 

Keeping your eyes closed, you lowered yourself further into the water so as it covered your mouth. This whole situation was so bizarre and you suddenly wondered what exactly you had gotten yourself into. 

Opening your eyes again, you met eyes with Sans who was just a few feet away from you, mimicking you with how far he was underwater. You took in a deep breath, lowering your head underwater. You titled back your head and savoured the cool feeling of the water before coming back up. You ran your hands over your face and through your hair and when you looked back ahead of you, Sans was only about a foot away. 

He just kind of looked at you. For once, it didn't seem like he had anything to say. His eyelights had come back, but they were a softer white that you've never seen before. 

There was another long stretch of silence, save for the small laps of water that swayed your body back and forth.

"...You ever been with a human before?" Maybe that was a dumb question to ask, but you started to wonder how this would work. Whatever… 'this' was.

Sans paused. "no," he said simply.

You swallowed. "I've, uh… never been with a monster, so…" 

"so?"

"I just… I-I know they do stuff differently, so… i don't know."

He smirked. "what exactly you plan on us doin' out here?"

"...Not sure," you said honestly. "I just don't want some weird magic shit to happen and freak out because you didn't warn me."

He chuckled. "now i kinda don't wanna tell you."

You glared. "Don't be a jackass about it."

"some freaky shit happens."

"...Like what?"

"you know. tentacles, for one. shapeshifting. s'worse when the full moon is up, so you lucked out there."

Your glare deepened.

He rolled his eyes, but his smirk didn't falter. "look, hon. i gotta tongue. i gotta…" he glanced at something under the water, looking somewhat bashful. "well, you kinda already saw what i have."

You blushed as well, sinking further under the water. You were suddenly much more nervous about this.

"So… just the usual? No reason to worry?"

"no reason ta worry." He repeated.

You never thought you'd find yourself trusting that dark, rough voice of his.

You nodded. 

Sans went to say something else, but was cut short but you swimming forward and almost completely closing the gap between the two of you. You gently placed a hand on his chest, curiously tracing your fingertips along his bones. They were much thicker than a human's and much more malleable. It was so unreal actually touching a living skeleton and even more so that you were kind of into it.

You flinched when he placed a hand on your waist, pulling you a little closer.

"This is alright, right?" You looked up at him. "Sorry I uh, kinda just threw this at you all of the sudden."

"sweetheart," he breathed, leaning in so close that your mouths were practically touching. "i'm so fucken horny that if you say another word i might just go insane." 

Your eyes widened at the response, your face somehow heating up even more. The sound of his voice rumbling so close to you awakened something that you hadn't felt in a long time. 

You nodded, licking your lips before pressing them against his teeth. 

Then he was immediately on you.

His hands desperately trailed up your back, his waist pressing up against yours. He kissed you back, his warm tongue slipping past your lips to trail along your teeth. His own teeth were almost comically sharp, but he seemed in practice enough to not cut you.

His body was so incredibly warm that it heated the water around you, rising to your core and making it feel like you dipped into a nice bath. It radiated off of him in waves strong enough you had to conclude it was magic.

He kissed you rough and sloppily, hard enough to push you back into deeper water. 

You had never felt like someone wanted to fuck you so badly and you were living for it.

You relished in his warmth as his hands clumsily fumbled with your bra strap, eventually separating the two ends and pulling it off of you. Your hands trailed up and down his body, weaving in and out of bones covered in mysterious scars that you'd maybe ask about later. Your hands made their way to the top of his boxers--which, again, you wouldn't have guessed him to have before tonight--shakily hesitating.

You were a bit rusty with all of this, so it was a bit nerve-wracking, but seeing how desperate Sans was, you couldn't bring yourself to care for too long.

You dipped your hand below the strap of his underwear, cupping a long, warm member that was nestled inside. 

Sans' body lurched forward, and he buried his face into your neck in response.

You used your free hand to pull down his boxers, letting his length rest in your other hand, fully erect and begging to be touched. He grunted and gripped your skin tightly when you gave his penis a long stroke with your palm. It was surprisingly normal, despite not having hair. Doable length with a pleasantly inviting girth.

Sans grit his teeth, grinding up against your hand. You might've taken the time to tease him if your own crotch wasn't pulsing with anticipation. 

You took the time to slip off your own panties, gently holding Sans' dick and readying yourself for impact.

"c'mon," he moaned, tightly holding the sides of your face. He opened his eyes and looked into yours. His eyelights were fuzzy and dim and he seemed to have trouble maintaining eye contact with you for even these few seconds.

Without looking away, you pressed his tip against your entrance and moved your hips forward to slide him inside of you. You looked intently into his eyes but Sans looked away the moment you surrounded him. His eye lights went dark as he started pumping in and out and you watched him quickly unravel. 

You lifted a leg and pressed harder against him, letting the water do the heavy lifting of your body while Sans kept you steady. 

You both moved faster and harder as you reached the edge, any noises that escaped either of your mouths drowned out from the lapping of water. 

You came before Sans did, letting your body collapse against his as he rode you through your orgasm. He came just as yours ended, and you caught a second wind at the feeling of the hot liquid coating your insides. You both kept going until Sans' orgasm subsided and he ran a hand over his sweaty skull, pulling himself out of you.

You caught your breath, pulling him in for a slower, softer kiss that he hesitantly returned. 

"Everything you thought it would be?" You laughed.

"fucking you?" He nodded. "hell yeah."

"I meant fucking a human," you grinned. "Unless… you thought about this before?" It was a joke, but your eyes widened when he looked caught off guard. "Wait."

"what?" He spat defensively.

You paused, taking a moment to connect the dots. "...Sans, when I walked in on you, were you--"

"no," he interrupted unconvincingly. 

You broke into a smug smile.

"i wasn't--fuck off!"

You couldn't help but be a little flattered. 

Sans huffed out an annoyed breath. "find your underwear yourself, i'm goin' back inside."

"Hey, no you don't!" You grabbed his hand, tugging him back. "How about… you help me fetch my clothes and we… head back inside for round two?"

He looked surprised at the offer, but shook away the expression. "fine. whatever."

You laughed, watching him grumble angrily as he splashed around the lake in search for your abandoned underwear.

Maybe this trip wouldn't be so bad afterall.


End file.
